Shear-thickening compositions

ABSTRACT

Shear-thickening aqueous compositions useful as workover fluids in producing or injection wells, as water diversion agents and mobility control fluids in post-primary oil recovery operations, and as hydraulic fracturing fluids well stimulation treatments are provided comprising the reaction product formed from a high molecular weight polyalkylene oxide polymer and a synthetic resin produced from aldehydes and phenols in an alkaline environment.

This application is a division of copending application having Ser. No.868,965, filed Jan. 12, 1978, now U.S. Pat. No. 4,212,747.

This invention relates to shear-thickening fluid compositions. Inaccordance with another aspect, this invention relates toshear-thickening fluid compositions prepared from a high molecularweight polyalkylene oxide polymer and a synthetic resin of an aldehydeand a phenol which composition is prepared in an alkaline environment.In accordance with a further aspect, the shear-thickening aqueouscompositions of the invention are useful as workover fluids in producingor injection wells, as water diversion agents and mobility controlfluids, and as hydraulic fracturing fluids.

Accordingly, an object of this invention is to provide novelshear-thickening fluid compositions.

A further object of this invention is to provide shear-thickening fluidcompositions having utility in the treatment of subterranean formations.

A further object of this invention is to provide shear-thickening fluidcompositions having utility in oil recovery operations.

Other objects and aspects, as well as the several advantages of theinvention, will be apparent to those skilled in the art upon a readingof the specification and the appended claims.

In accordance with the present invention, a novel shear-thickening fluidcomposition is prepared by contacting a high molecular weightpolyalkylene oxide polymer, such as polyethylene oxide, with a syntheticresin comprising the reaction product of an aldehyde with phenoliccomponents, such as phenol and/or resorcinol, in the presence of aqueousalkali.

In accordance with another embodiment, the shear-thickening inventivecompositions can be prepared by contacting phenolic component(s),aldehyde, and polyalkylene oxides in aqueous solution under suitablereaction conditions.

The inventive compositions described herein containing water, a highmolecular weight polyalkylene oxide, and, e.g., a phenolformaldehydesynthetic resin, are highly viscoelastic, i.e., such mixtures are fluidin a quiescent state but assume a gel-like character on agitation. Afteragitation is stopped, the gel-like character disappears and thecomposition returns to the original fluid state. Fluids exhibiting suchshear-thickening behavior are well recognized in the art and are usefulas workover fluids in producing or injecting wells, as water diversionagents and mobility control fluids in postprimary oil recoveryoperations, and as hydraulic fracturing fluids in well stimulationtreatments.

As water diversion agents and mobility control fluids the inventivecompositions can be injected at so-called injection wells, respectively,to correct the permeability profile of a formation or for mobilitycontrol in post-primary oil recovery operations. Said compositions canfunction as permeability correction agents by temporarily plugging"thief zones" (high permeability areas), and thus direct thesubsequently injected drive fluids to the less permeable, relativelyoil-rich zones. The effectiveness of such agents is reflected by themagnitude of the increase observed in the oil-to-water ratio atsurrounding production wells. Said compositions can function as mobilitybuffers, e.g., in surfactant flooding by injecting said compositions asviscous slugs to push the previously injected surfactant slug andrecovered oil to a producing well. The viscosity of the mobility controlfluid relative to that of the surfactant slug is such that little or nofingering of said slug into said surfactant slug takes place.

Hydraulic fracturing is commonly employed to increase the production offluids from subterranean formations. Hydraulic fracturing comprises theinjection of a suitable fracturing fluid down a well penetrating aformation and into said formation under sufficient pressure to overcomethe pressure exerted by the overburden. This results in creating a crackor fracture in the formation to provide a passageway which facilitatesflow of fluids through the formation and into the well. Propping agentscan be included in the shear-thickening compositions of the invention ifdesired. Propping agents which can be used include any of those known inthe art. e.g., sand grains, walnut shell fragments, tempered glassbeads, aluminum pellets, and similar materials, so long as they meet theappropriate compatibility requirements. Generally speaking, it isdesirable to use propping agents having particle sizes in the range of 8to 40 mesh (U.S. Sieve Series). However, particle sizes outside thisrange can be employed.

A common problem in hydraulic fracturing involving the use ofwater-based compositions is the excessive loss of fluid to theformation. This significant loss of fluid, primarily water, to theformation, e.g., can prevent the attainment of sufficiently highpressures necessary to fracture selected zones of the formation. Fluidloss into the formation can be lessened, e.g., by adding ashear-thickening fluid such as disclosed herein. Said shear-thickeningfluids can be used in fracturing or added to suitable fracturing fluidsto function as fluid-loss control additives therein. Apparently,fluid-loss additives decrease the transfer of water into the formationby temporarily plugging and/or plastering the exposed faces of the moreaccessible channels and passages in the formation.

The synthetic resins that can be used can be prepared in accordance withknown methods and generally comprise the reaction of a suitable aldehydewith a suitable phenol compound in the presence of an alkaline catalyst.The molar ratio of aldehyde to phenol is generally in the range of 0.1:1to 2:1 with a preferred range of about 0.3:1 to 1:1. The pH maintainedduring the preparation of the synthetic resin is in the range of about 7to 12, preferably in the range of about 9 to 11.

Suitable aldehydes that can be employed include those having from one tofour carbon atoms such as formaldehyde, acetaldehyde, butyraldehyde, andthe like. Suitable phenols include phenol, catechol, resorcinol, thecresols, and the like with the proviso that catechols are operable onlyin brine-containing systems. Suitable alkaline catalysts for thephenol-aldehyde condensation are selected from the alkali metal andammonium hydroxides and carbonates with sodium hydroxide and sodiumcarbonate being preferred because of cost and availability.

The shear-thickening inventive composition can also be prepared bycontacting the phenol, aldehyde, polyalkylene oxide under suitableconditions in an aqueous reaction medium (see Example II herein).

The synthetic resin-forming reaction mass is maintained in the broadtemperature range of 100° F. to 212° F., preferably 120° F. to 180° F.,for a time in the range of 5 minutes to 48 hours, preferably 10 minutesto 24 hours, and most preferably 10 minutes to one hour.

Alternatively, the shear-thickening inventive compositions can beprepared by reacting the phenolic component and aldehyde component in athickened aqueous solution of the polyethylene oxide over a pH range ofabout 7 to 9. The ranges of component concentrations for such aprocedure are shown below:

    ______________________________________                                                    Concentration Ranges (ppm)                                        Components    Broad        Preferred                                          ______________________________________                                        Polyalkylene oxide                                                                          1,000 to 30,000                                                                            5,000 to 20,000                                    Phenolic compound                                                                           200 to 20,000                                                                              500 to 10,000                                      NaHCO.sub.3 (optional)                                                                      0 to  5,000  1,000 to  3,000                                    HCHO (dry basis)                                                                            100 to  5,000                                                                              1,000 to  3,000                                    ______________________________________                                    

As disclosed in the art, synthetic phenol-aldehyde resins are preferablyand most commonly produced, e.g., by condensation of phenol and/orresorcinol with formaldehyde in aqueous alkaline solution. The specificnature of the resulting condensation product is a function of therelative amounts of phenol and formaldehyde, the reaction temperatureand reaction time as well as the nature and quantity of alkalinecatalyst. In regard to the instant invention, a relatively low degree ofadvancement or polymerization of the resulting condensation product isdesired so that relatively short reaction times and lower temperaturesare highly desirable. A useful resin solution exhibits a comparativelylow viscosity; thus, it may be useful to monitor the viscosity of saidresin-forming reaction mixture in order to obtain compositions suitablefor use in the instant invention. The polymerization reaction isconveniently quenched by rapidly decreasing the temperature of thereaction mass as the viscosity thereof is in a range suitable for use inthe shear-thickening fluids described herein.

The term "polyalkylene oxide polymer" as used herein is meant to includehigh molecular weight polyethylene oxides, polypropylene oxides, andpolybutylene oxides, etc. These polyalkylene oxides can be chemicallymodified, desirably to obtain improved results, and the chemicallymodified polyalkylene oxide polymers are intended to be within the scopeof this invention. The molecular weight of the polyalkylene oxidepolymers is about 10,000 to 10,000,000 or more, and preferably about600,000 to about 7,500,000, and more preferably about 4,000,000 to about6,000,000. Lower or higher molecular weight polymers may be desired forparticular purposes; but the above ranges should be suited for mostapplications. The preferred polyalkylene oxide is commercially availablefrom Union Carbide Company, 270 Park Avenue, New York, NY 10017, U.S.A,under the trademarks "Polyox Coagulant" and "Polyox WSR 301."

The aqueous medium can be soft, brackish or brine water. Preferably thewater is soft, but it can contain salts which are preferablycharacteristic of those within the subterranean formation beingfractured. Where a highly viscous fluid is desired, it is preferred touse the soft water.

The amount of synthetic phenol-aldehyde resin and polyalkylene oxidepolymer used will vary somewhat but will be sufficient to provide ashear-thickening composition. In general, the amount of synthetic resinwill range from 0.025 to 2.5 weight percent, and the amount ofpolyalkylene oxide polymer will range from 0.1 to 3.0 weight percent,with the balance being water.

Any suitable method can be employed for preparing the shear-thickeningcompositions of the invention. It is ordinarily preferred to firstdissolve or disperse the polymer in water before contracting the polymersolution with the alkaline synthetic phenol-formaldehyde resin reactionmixture. Alternatively, the phenol and formaldehyde can be reacted toform the synthetic resin in an aqueous solution containing saidpolyalkylene oxide, said phenol, and said aldehyde. It is within thescope of the invention to moisten or slurry the polymer with a smallamount, e.g., about one to about six weight percent based on the weightof the polymer, of a low molecular weight alcohol, e.g., C₁ to C₃alcohols, as a dispersion aid prior to dispersing the polymer in water.It is preferred that there be no undue delay between completing thepreparation of the shear-thickening composition and its introductioninto contact with the formation.

The shear-thickening compositions of the invention can be prepared onthe surface in a suitable tank equipped with suitable mixing means, andthen pumped down the well and into the formation employing conventionalequipment for such shear-thickening pumping compositions. However, it iswithin the scope of the invention to prepare said compositions whilethey are being pumped down the well. This technique is sometimesreferred to as "on the fly." For example, a solution of the polymer inwater can be prepared in a tank adjacent the wellhead. Pumping of thissolution through a conduit to the wellhead can then be started. Then, afew feet downstream from the tank, a suitable connection can be providedfor introducing the synthetic phenol-formaldehyde resin reaction mixturepreferably as an aqueous solution. As will be understood by thoseskilled in the art, the rate of introduction of said components intosaid conduit will depend upon the pumping rate of the shear-thickeningcomposition through said conduit. Mixing orifices can be provided insaid conduit, if desired.

It is within the scope of the invention to precede the injection ofshear-thickening composition into the well and out into the formationwith a preflush of a suitable cooling fluid, e.g., water. Such fluidsserve to cool the well tubing and formation and extend the usefuloperating temperature range of said compositions. The volume of saidcooling fluid so injected can be any suitable volume sufficient tosignificantly decrease the temperature of the formation being treatedand can vary depending upon the characteristics of the formation. Forexample, amounts up to 20,000 gallons or more can be used to obtain atemperature decrease in the order of 100° F. to 250° F.

The following examples will serve to further illustrate the invention,but they should not be considered as unduly limiting on the invention.

EXAMPLE I

A low molecular weight phenol-aldehyde synthetic resin was prepared byplacing a charge of 5 g (0.045 mol) resorcinol, 4.3 g (0.046 mol)phenol, and 3.7 g (0.092 mol) sodium hydroxide in 50 ml water andheating to 130° F. to effect solution. A 3.4 ml (0.046 mol) HCHO sampleof 37 weight percent formalin solution was added, and the temperature ofthe reaction mass was increased to 175° F. and maintained at thattemperature for 15 minutes. The reaction mixture was cooled to roomtemperature, and one-fifth of this mixture was added to a 250 ml portionof an aqueous solution of polyethylene oxide (5,000 ppm of UnionCarbide's Polyox WSR 301). This inventive composition was tested with aModel 35 Fann Viscosmeter, and the results are shown in Table I toillustrate to shear-thickening character of the inventive composition.

                  TABLE I                                                         ______________________________________                                        Viscosity Measurements in a                                                   Shear-Thickening Composition                                                  Viscosity (cp) at Shear Rate sec.sup.-1                                       10.2     171       342       511     1022                                     ______________________________________                                        NR.sup.a 21        18        17      125.sup.+                                ______________________________________                                         .sup.a Nr represents not recorded.                                       

The high viscosity value of 125⁺ cp at a shear rate of 1022 sec⁻¹demonstrates the shear-thickening character of the inventive compositionand indicates the potential usefulness of such inventive compositions asoil well treatment fluids.

EXAMPLE II

An inventive shear-thickening composition was prepared in aqueoussolution at a pH of 7.6 by combining the following components in theindicated quantities: polyethylene oxide (WSR 301), 15,000 ppm;resorcinol, 1,000 ppm; NaHCO₃, 2,000 ppm; and HCHO (as formalin), 2,000ppm; and the aging this mixture for 24 hours at 125° F. Theshear-thickening character of this inventive composition was verified bytesting in a Stormer viscometer. Such a composition is potentiallyuseful as an oil well treatment fluid.

I claim:
 1. A process for hydraulically fracturing a subterraneanformation penetrated by at least one well which comprisesinjecting intothe formation at a pressure sufficient to fracture the formation anaqueous shear-thickening composition containing as essentialingredients:(a) a small but effective amount in the range of 0.1 to 3weight percent of a high molecular weight polyalkylene oxide selectedfrom the group consisting of polyethylene oxides, polypropylene oxides,and polybutylene oxides having a molecular weight of about 10,000 toabout 10,000,000 and (b) a small but effective amount in the range of0.025 to 2.5 weight percent of a synthetic resin comprising the reactionproduct formed by heating an aqueous alkaline mixture of an aldehydehaving from one to four carbon atoms and a phenol compound selected fromthe group consisting of phenol, catechol, resorcinol and cresol at areaction temperature in the range of 100° F. to 212° F. for a period oftime in the range of 5 minutes to 48 hours and a molar ratio of aldehydeto phenol in the range 0.1:1 to 2:1 and a pH of about 7 to 12,theamounts of (a) and (b) being sufficient to form a shear-thickeningcomposition that is fluid in a quiescent state but becomes gel-like incharacter on agitation, and (c) the balance of the composition beingwater maintaining said composition in said formation in contacttherewith for a period of time sufficient to significantly increaseformation permeability and fracturing said formation to stimulate theproduction of fluids therefrom.
 2. A process according to claim 1wherein (a) has a molecular weight range of 600,000 to 7,500,000.
 3. Aprocess according to claim 1 wherein a propping agent is incorporatedinto said aqueous shear-thickening composition.
 4. A process accordingto claim 1 wherein a cooling fluid is injected into the formation toreduce the temperature of the formation prior to introduction of saidaqueous shear-thickening composition.
 5. A process according to claim 1wherein(a) is a polyethylene oxide and (b) is the reaction productformed from formaldehyde and phenol.
 6. A process according to claim 1wherein(a) has a molecular weight range of 4,000,000 to 6,000,000 and(b) is a synthetic resin formed by heating a mixture of formaldehyde andphenol or resorcinol.